Q1 and 2, what Andy said.
Q3, just set up a share each machine. Open Windows explorer, view explorer bar folders. Open up my computer and c: and either create a new directory or share an existing one. To share it right click sharing, give it a share and set permissions. The other machine can either browse to it when you open my network places, entire network .... or you can map a drive \\<pc name>\<share name>
Q4 the only way I know is to set up your own mail server to store mail in a central place. Not hard to do, but you'll have to always have it powered up.